Lighting unit for lighting airfields

ABSTRACT

The invention relates to a lighting unit for lighting airfields on an airport, in particular for delivering signals to an airplane. It comprises a light source, which has at least one light-emitting diode for generating light to be emitted, electrical components for supplying and actuating the light source, optical components for influencing the light generated by the light source, and an outer housing for receiving the light source and the electrical and optical components, which has a light exit opening through which light influenced by the optical components exits. According to the invention, the light source is arranged with the electrical and optical components in a cassette module closed in a gas-tight manner. Said module is integrated in the outer housing, wherein the outer housing is likewise closed in a gas-tight manner, so that the components disposed in the cassette module have double sealing protection.

This invention relates to a lighting unit for lighting airfields at anairport, in particular for signaling an aircraft, having the features ofthe preamble of patent claim 1. Such lighting units are used forlighting airfields at airports, e.g. for signaling aircraft in approachor taxiing on a tarmac or taxiway, in particular airplanes orhelicopters. A distinction is made e.g. between approach lighting,take-off and landing runway lighting, and taxiway lighting. The lightemitted by a lighting unit when signaling must then comply with acertain spatial intensity distribution specified by internationalstandards and released by organizations for standardization, such asICAO, short for International Civil Aviation Organization, or FAA, shortfor Federal Aviation Administration.

From the product literature “LED—Taxiway Centre Line, Stop Bar andIntersection—Medium Intensity—Inset Light”, published by ADB—A SiemensCompany, under order number E10001-T95-A103-V1-7600, a flush-mountedinset light for taxiway centre lines and stop bars is known, wherebyinside a housing made of aluminum alloy, optical components, such aslight emitting diodes, collimators, and prisms, as well as electricalcomponents, such as cable connectors, transformers, and circuit boards,are arranged in a distributed manner. Toward the outside, the housing issealed from water penetration by means of a labyrinth seal betweenhousing cup and housing cover, and by means of prism seals in the lightexit openings of the cover. For each of the the various signals severallight emitting diodes are provided, which, during assembly at themanufacturing plant, have to be manually aligned with respect to theother optical components so as to generate the required light emissionintensity profile .

The utility model specification DE 203 09 405 U1 discloses aflush-mounted inset light, which has a housing with a housing baseembedded in the ground and a housing cover closing said base from above.The housing cover has two openings, into each of which a module isincorporated from above comprising a module top and a module bottomsealingly screwed thereto. Prisms are inserted into the lighttransmission openings of the module top. Three light emitting diodeswith optics are collectively attached to a board screwed to the modulebottom. The power supply of the light emitting diodes is provided forvia a cable which is sealingly guided into the module through anopening. The cable is connected to a converting unit located inside thehousing and connected to a supply cable. The modules are pre-assembledfor the assembly of the flush-mounted inset light.

Patent publication DE 198 37 224 A1 discloses a lighting unit forlighting airfields with light emitting diodes as light sources formingseveral clusters. The clusters are integrated into a cassette arrangedabove the power supply and control device of the lighting unit. The basebody respectively the housing of the cassette is entirely or partiallyfilled with a dielectric material so that there are no cavities insidethe cassette and they are inherently watertight and gastight.

Water penetrating into the housing of a lighting unit, for instance inthe area of the prism of a flush-mounted inset light, may damage boththe electrical and the optical system. Leakage of the lighting unit mayas well occur during operation because of worn out components or ageingseals due to vibrations or direct overrun loads and followingmaintenance works due to defective closing of the housing when nosealing test is performed.

Maintenance work requiring an optical element to be removed or replacedimplies the risk of defective assembly also with regard to the exactmounting position and the mutual alignment of the optical elements. Thisis all the more critical the fewer light sources are provided for agiven signal of the lighting unit, as there is a risk that the requiredstandard high precision intensity distribution of the emitted light canno longer be maintained.

Consequently, the underlying aim of the invention consists in providinga lighting unit of the type mentioned previously, requiring littleassembly and maintenance effort and having a high fail safety.

According to the invention, the object is achieved by a generic lightingunit having the features indicated in the characteristics of claim 1.Accordingly, the light source has at least one light emitting diode andis arranged inside a gastightly closed cassette module together with theelectrical and optical components. The cassette module is integratedinto the outer housing of the lighting unit. The outer housing willprovide the cassette module protection against the impact of externalforces, and is also gastightly closed so that the components arrangedinside the cassette module may benefit from double sealing protection.

This design offers the advantage that, if the outer housing is damaged(e.g. a crack in the light exit window) the cassette module will remainintact. Thus, water or moisture may well penetrate into the outerhousing, but not into the cassette module. As the electrical componentsfor controlling the light emitting diodes are arranged inside thegastight cassette module, damage to the outer housing will not badlyaffect the light source inside the cassette module, thereby eliminatingthe risk of failure of the light source.

The light exit opening of the outer housing may also comprise a windowmodule, which depending on the application of the lighting unit isformed as a prism, a scattering unit, or else as a glass cover withoutany additional optical functionality. This window module is gastightlyinserted into a light exit opening of the outer housing.

The cassette module has an opening, in which a transparent windowelement for radiating light is gastightly inserted. The window elementhas an optical element for affecting the beam shape and/or radiatingdirection of the exiting light beam. The optical element may, forexample, be formed by a collimating device and/or a scattering deviceand/or a lens device or a combination of such devices. The at least onelight emitting diode and the optical element are thereby positioned withrespect to each other for generating a required intensity distributionof the emitted light and secured in mutual alignment.

The window module of the outer housing is distinct from the windowelement of the cassette module.

By using light emitting diodes as a light source the average time to thefirst failure thereof is significantly extended in comparison withtraditional incandescent light sources, which corresponds to providing amaintenance-free light source. Therefore, maintenance work can beperformed on the lighting unit without the gastight cassette modulehaving to be opened, thereby eliminating the risk of a general failureof the electrical or optical components of the lighting unit due towater penetration. The cassette module as such is also virtuallymaintenance-free. As assembly and integration of the electrical andoptical components into the cassette module as well as their sealing areperformed by the manufacturer, product liability for sealing of thecassette module can be taken over by the manufacturer. The number oflight emitting diodes used decreasing down to one mere light emittingdiode, requires precise positioning with respect to other opticalcomponents, which is ensured by the manufacturer's specialists. Thecassette module can be used for lighting units for unidirectional,bidirectional, and even omnidirectional light emission. The lightingunit can thereby be formed as both flush-mounted inset light and surfacelight. The cassette module is gastightly closed by means of an adhesive,in particular a UV curing adhesive, silicone rubber, or any othersealing element.

In a preferred configuration of the lighting unit according to theinvention, the cassette module has a module housing receiving theelectrical components and a module lid closing the module housing, whichmodule lid comprises the opening with the gastightly inserted windowelement. The module lid can for instance be produced separately andincludes a seal against water penetration, and the window element withthe optical elements for affecting the beam, which are positioned andsecured in alignment with respect to the light emitting diodes.

In a preferred embodiment of the lighting unit according to theinvention, markings and/or mechanical mounting aids are provided, bymeans of which the light emitting diodes and the window element with theoptical element can be positioned with respect to each other and can besecured in mutual alignment. The window element, for example, hasmarkings allowing for an optimally aligned assembly with the circuitboard of the light emitting diodes. Here, the above-described possibleoptimal intensity distribution is virtually achieved through activealignment. Preferably, this is applied for each window element whenseveral signals are produced.

In an advantageous configuration of the lighting unit according to theinvention, the module housing and/or the module lid and/or an outershell of the cassette module are formed to have high thermalconductivity. As a result, the heat generated by the light emittingdiodes and other electrical components can be released to theenvironment. This is advantageous because efficiency and durability ofthe light emitting diodes increase when the maintained operatingtemperature decreases.

Preferably, the window element and the module lid of the cassette moduleof the lighting unit according to the invention are formed to beone-piece and transparent. This one-piece component can be made out ofpolycarbonate. As a result, it is advantageously possible to keep a lownumber of parts for a lighting unit according to the invention.Furthermore, separately connecting and sealing the window element andmodule lid are avoided.

In another advantageous embodiment of the lighting unit according to theinvention, the light source is formed for generating light for varioussignals, wherein only a few light emitting diodes or merely one lightemitting diode is/are associated with each signal. As light emittingdiodes, preferably high performance light emitting diodes come intoconsideration, through which electrical currents of an intensity of 0.1A to at least 3.0 A are flowing, having a heat resistance of e.g. atleast 8 K/W, and emitting a light current of at least 20 lto 150 lm.Depending on the application, the high performance light emitting diodecan have a Lambert, Batwing, or side radiation characteristic. Thisallows for several signals to be combined with a single window element,which is particularly advantageous for lighting units for signal outputhaving a low form factor.

Thereby, the light emitting diodes are preferably arranged on a circuitboard, and formed depending on the signal to be emitted, for generatinglight in the visible spectrum, in particular blue, green, yellow,orange, red or white light, or light in the infrared spectrum. Thecolour white can then be generated by phosphor inversion and/or an RGBmixing technique. It is also possible to use large surface radiatinglight emitting diodes. Through infrared radiation, aircraft fitted withinfrared sensors can detect the infrared light emitted by the lightingunits, as is already the case with halogen lamps.

In another advantageous configuration of the lighting unit according tothe invention, the light emitting diodes are arranged on a circuit boardhaving an optical element for affecting the beam. The optical elementsconnected to the light emitting diodes can advantageously already bealigned with respect to each other by the manufacturer.

In another preferred configuration of the lighting unit according to theinvention, the window element and/or the circuit board have opticalelements for affecting the beam for each signal to be emitted. Dependingon the signal, some optical elements may strongly focus a light beam,while other optical elements of about the same window element may widelyfan out a light beam.

In another preferred configuration of the lighting unit according to theinvention, a power supply line is gastightly inserted into the cassettemodule for connecting the electrical components to an external powersource. The power source may be a constant current source or else aconstant voltage source.

In another advantageous embodiment of the lighting unit according to theinvention, the cassette module is filled with an inert gas. Hereby, adry atmosphere can be created inside the cassette module preventingcondensation-induced failure of the electrical or optical components.

In another preferred configuration of the lighting unit according to theinvention, a desiccant is introduced into the cassette module. As aresult, residual humidity, which may otherwise condense, will be bound,in particular when using light emitting diodes which hardly produce anywaste heat. Condensed water vapour might deposit on optical componentsas a dispersive layer reducing light exit.

Further properties and advantages of the lighting unit according to theinvention are presented in the following description of an exampleembodiment represented in the drawings, in which

FIG. 1 schematically shows a cross-section through a gastight cassettemodule,

FIG. 2 and FIG. 3 schematically show circuit boards with light emittingdiodes of a lighting unit according to the invention,

FIG. 4 schematically shows an exploded representation of a flush-mountedinset light according to the invention.

According to FIG. 1, a gastight cassette module 1 for integration into anot fully represented lighting unit according to the invention, which isnot represented, has a module housing 2 and a module lid 3. In themodule housing 2, a light source formed of light emitting diodes 4 andelectrical components 5 are arranged comprisingpower lines and a drivercircuit for driving the light emitting diodes 4, which are notrepresented in great detail. The module housing 2 is made of a materialexhibiting high thermal conductivity for releasing the heat generatedduring operation of the electrical components 5 to the environment. Themodule lid 3 is produced in one piece from optically transparentpolycarbonate and has a translucent window element 6. On the windowelement 6, optical elements 7 are moulded, which are formed foraffecting the beam shape and/or beam direction of the light generated bythe light emitting diodes 4. The optical elements 7 are not representedin detail and can have devices for light focusing, scattering,diffracting, reflecting, and the like.

For the manufacturing of the gastight cassette module 1, the module lid3 is glued to the module housing 2. Thereby, the module lid 3 and themodule housing 2 are assembled by means of an adhesive, e.g. by means ofa UV curing adhesive or silicone rubber, wherein the light emittingdiodes 4 are actively positioned and aligned in relation to the opticalelements 7. While position and alignment are being maintained theadhesive is allowed to cure. Thereby, position and alignment areoriented according to the optical axis of the light emitting diode 4 inorder to achieve optimum intensity distribution of the emitted light.This is characterized by maximum peak intensity together with a veryminimum full width at half maximum. Furthermore, the optimum intensitydistribution will cause minimum optical losses. Thereby, positioning andalignment can also be performed with an active mounting aid, by means ofwhich all degrees of freedom of movement can be set in a motorisedmanner.

Alternatively, the module housing 2 can be gastightly closed by means ofthe module lid 3, e.g. by implementing an O-ring.

According to FIG. 2 and FIG. 3, the light source consists of a circuitboard 8 fitted with light emitting diodes 41 to 43. Thereby, differentlight emitting diodes 41 to 43 are provided for each signal to beemitted by the lighting unit. Preferably, a single high performancelight emitting diode is provided for each signal. If the various signalsfor instance a green clearance signal and a red stop signal at a stopbar on a taxiway before a runway junction require different intensitydistributions, then the window element 6 has different optical elements7 depending on the signals. The optical elements 7 can also be arrangedon circuit board 8 above the light emitting diodes 41 to 44. The lightemitting diodes 43 represented in FIG. 2 and FIG. 3 to the right, forinstance emitting red light, have an optical element of larger curvatureon the light exit surface, which are thus less dispersive, while in thelight emitting diodes 41 or 42 respectively represented to the left andfor instance emitting green light, the light emitting diode 41 of FIG. 2has a lower curvature on the light exit surface than the light emittingdiode 42 represented in FIG. 3.

FIG. 4 shows an exploded representation of a lighting unit 10 accordingto the invention. The cassette module 1 is placed in an outer housingmade up of a inset base 11 or a mounting pot and an adapted lid, ingeneral both made of aluminum.

The lighting unit represented in FIG. 4 is a flush-mounted inset light.The inset base 11 is typically fastened in the ground, in concrete orasphalt by means of an adhesive.

The holes 15 for cables entering into the inset base 11 are gastightlyclosed. Gastight sealing is ensured for instance by a rubber seal 13between the inset base 11 and the lid 12.

The gastightly closed cassette module 1, which comprises the lightsource as well as the electrical components for supplying and drivingthe light source and the optical components 7 for affecting the lightgenerated by the light source, fits into the inset base 11 and under thelid 12. The lid 12 comprises light exit openings 14 through which thelight affected by the optical components 7 of the cassette module 1exits. The light exit openings 14 can be made from a prism or any othertransparent element inserted into an opening of the lid 12 andgastightly closed.

The advantage of the lighting unit according to the invention is that ifthe prism 14 is broken, e.g. if it is damaged by a pebble projected byan air stream of the airplane driving mechanism, the cassette module 1will remain intact so that the light source, as well as the optical andelectrical components remain protected against weather effects, such ashumidity.

1. A lighting unit for lighting airfields at an airport, in particularfor signaling an aircraft, comprising a light source for generatinglight to be radiated and having at least one light emitting diode,electrical components for supplying and steering the light source,optical components for affecting the light generated by the lightsource, and an outer housing for receiving the light source as well asthe electrical and optical components, the outer housing having a lightexit opening through which light affected by the optical components willexit, wherein the lighting unit comprises a gastightly closed cassettemodule, in which the light source is arranged together with the opticalcomponents, wherein the electrical components are equally arrangedinside the gastightly closed cassette module, the cassette module has anopening into which a transparent window element for radiating light isgastightly inserted, which has an optical element for affecting the beamshape and/or radiation direction of the exiting light beam, and whereinthe light emitting diode and the optical element are positioned withrespect to each other and secured in mutual alignment for generating arequired intensity distribution of the radiated light, and the cassettemodule is integrated into the outer housing, wherein the outer housingis also gastightly closed, so that the components arranged inside thecassette module benefit from double tightness protection.
 2. Thelighting unit according to claim 1, wherein the light exit opening ofthe outer housing has a window module which is distinct from the windowelement of the cassette module.
 3. The lighting unit according to claim1, wherein the cassette module has a module housing receiving theelectrical components and a module lid closing the module housing andcomprising the opening with the gastightly inserted window element. 4.The lighting unit according to claim 1, wherein markings and/ormechanical mounting aids are provided, by means of which the lightemitting diodes and the window element with the optical element can besecured so that they can be positioned with respect to each other andmutually aligned.
 5. The lighting unit according to claim 2, wherein themodule housing and/or the module lid and/or an external shell of thecassette module are formed to have high thermal conductivity.
 6. Thelighting unit according to claim 2, wherein the window element and themodule lid of the cassette module are formed to be one-piece andtransparent.
 7. The lighting unit according to claim 1, wherein thelight source is made for generating light for various signals, whereinfew or just one light emitting diode(s) are/is associated with eachsignal.
 8. The lighting unit according to claim 7, wherein the lightemitting diodes are arranged on a circuit board and are formed accordingto the signal to be emitted for generating light in the visiblespectrum, in particular blue, green, yellow, orange, red, or whitelight, or light in the infrared spectrum.
 9. The lighting unit accordingto claim 1, wherein the light emitting diodes are arranged on a circuitboard having an optical element for affecting the beam.
 10. The lightingunit according to claim 1, wherein the window element has opticalelements for affecting the beam for each signal to be output.
 11. Thelighting unit according to claim 1, wherein a power supply line forconnecting the electrical components to an external power source isintroduced into the cassette module in a gastight manner.
 12. Thelighting unit according to claim 1, wherein the cassette module isfilled with an inert gas.
 13. The lighting unit according to claim 1,wherein a desiccant is introduced into the cassette module.
 14. Thelighting unit according to claim 1, formed as a flush-mounted insetlight.
 15. The lighting unit according to claim 9, wherein the circuitboard has optical elements for affecting the beam for each signal to beoutput.